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Inferred duration of infectious period of SARS-CoV-2: rapid scoping review and analysis of available evidence for asymptomatic and symptomatic COVID-19 cases
  1. Andrew William Byrne1,
  2. David McEvoy2,
  3. Aine B Collins3,4,
  4. Kevin Hunt5,
  5. Miriam Casey3,
  6. Ann Barber3,
  7. Francis Butler5,
  8. John Griffin4,
  9. Elizabeth A Lane3,4,
  10. Conor McAloon6,
  11. Kirsty O'Brien7,
  12. Patrick Wall8,
  13. Kieran A Walsh7,
  14. Simon J More3
  1. 1 One-Health Scientific Support Unit, Government of Ireland Department of Agriculture Food and the Marine, Dublin, Ireland
  2. 2 School of Public Health, Physiotherapy and Sports Science, University College Dublin, Dublin, Ireland
  3. 3 Centre for Veterinary Epidemiology and Risk Analysis, School of Veterinary Medicine, University College Dublin, Dublin, Ireland
  4. 4 Government of Ireland Department of Agriculture Food and the Marine, Dublin, Ireland
  5. 5 Centre for Food Safety, School of Biosystems and Food Engineering, University College Dublin, Dublin, Ireland
  6. 6 School of Veterinary Medicine, University College Dublin, Dublin, Ireland
  7. 7 Health Information and Quality Authority, Cork, Munster, Ireland
  8. 8 Department of Public Health, School of Public Health, Physiotherapy and Sports Science, University College Dublin, Dublin, Ireland
  1. Correspondence to Dr Andrew William Byrne; ecologicalepidemiology{at}


Objectives Our objective was to review the literature on the inferred duration of the infectious period of COVID-19, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus, and provide an overview of the variation depending on the methodological approach.

Design Rapid scoping review. Literature review with fixed search terms, up to 1 April 2020. Central tendency and variation of the parameter estimates for infectious period in (A) asymptomatic and (B) symptomatic cases from (1) virological studies (repeated testing), (2) tracing studies and (3) modelling studies were gathered. Narrative review of viral dynamics.

Information sources Search strategies developed and the following searched: PubMed, Google Scholar, MedRxiv and BioRxiv. Additionally, the Health Information Quality Authority (Ireland) viral load synthesis was used, which screened literature from PubMed, Embase, ScienceDirect, NHS evidence, Cochrane, medRxiv and bioRxiv, and HRB open databases.

Results There was substantial variation in the estimates, and how infectious period was inferred. One study provided approximate median infectious period for asymptomatic cases of 6.5–9.5 days. Median presymptomatic infectious period across studies varied over <1–4 days. Estimated mean time from symptom onset to two negative RT-PCR tests was 13.4 days (95% CI 10.9 to 15.8) but was shorter when studies included children or less severe cases. Estimated mean duration from symptom onset to hospital discharge or death (potential maximal infectious period) was 18.1 days (95% CI 15.1 to 21.0); time to discharge was on average 4 days shorter than time to death. Viral dynamic data and model infectious parameters were often shorter than repeated diagnostic data.

Conclusions There are limitations of inferring infectiousness from repeated diagnosis, viral loads and viral replication data alone and also potential patient recall bias relevant to estimating exposure and symptom onset times. Despite this, available data provide a preliminary evidence base to inform models of central tendency for key parameters and variation for exploring parameter space and sensitivity analysis.

  • epidemiology
  • virology
  • infectious diseases
  • public health

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  • Contributors AWB conducted the eligibility screening of shortlisted studies, extracted the data and conducted the analyses and completed the initial draft of the manuscript; SM was involved in conception and project coordination; ÁBC, KH and FB conducted the initial literature searches; DM, KOB and KAW conducted searches and screened shortlisted studies; AWB, SJM, ÁBC, KH, FB, DM, KOB, KAW, AB, JG, EAL, PW, CM and MC critically reviewed and commented/edited the paper. All authors read and approved the final manuscript.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

  • Patient consent for publication Not required.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement All data relevant to the study are included in the article or uploaded as supplementary information. The data used in this paper and code are presented in supplementary material 2 and 3; no additional data available.